Chemistry practice test 4

How many significant figures are there in the following figures?
i. 6*104
ii. 0.008320
iii. 4.05*10-2
iv. 100.0

1, 7, 5, 4

5, 6, 5, 3

1, 4, 3, 4

1, 7, 5, 3

1, 4, 3, 1

Correct Answer : c) 1, 4, 3, 4.

Explanation:

6*104 = 6000 has only one significant figure. Leading zeros are not significant, for 0.008320 it is 4. Zeros appearing anywhere between two non-zero digits are significant figures, for 4.05*10-2 = 0.00405, it is 3. Trailing zeros in a number containing a decimal point are significant, for 100.0 it is 4.

In a polyatomic species, the sum of oxidation numbers of the element in the ion _________ the charge on that species.

Is greater than

Is lesser than

Equals

Is either greater or lesser than

Is zero to

Correct Answer : c) Equals

Explanation:

The sum of oxidation numbers in polyatomic ion or species is equal to the charge of the ion. For example, the sum of the oxidation number for SO42- is -2.

Question 6

In which of the following processes, is the process always non-feasible?

ΔH>0, ΔS>0

ΔH<0, ΔS>0

ΔH>0, ΔS<0

ΔH<0, ΔS<0

ΔH=0, ΔS=0

Correct Answer : c) ΔH>0, ΔS<0

Explanation:

For a non-spontaneous or non feasible process, ΔH>0 and ΔS<0. For a spontaneous or irreversible reaction, ΔH<0 and ΔS>0. For an equilibrium or reversible process, ΔH=0 and ΔS=0.

Question 7

The hybridisation in NH4+ is

a) sp

b) sp2

c) sp3

d) sp3d

e) sp3 d2

Correct Answer : c) sp3

Explanation:

Number of valence electrons in N is 5 and in H it is 4.
So total number of valence electrons = 5 + 4 = 9; Charge = +1.
Therefore, total electrons in NH4+ = 9 - 1 = 8
When the total number of electrons is less than 8, divide by 2. If it lies between 9 and 56, divide it by 8.
8/2 = 4; X=4
Therefore, hybridisation in NH4+ is sp3.

Aprotic solvents do not solvate the anions effectively and it is used for SN2 reactions. Acetonitrile is the only aprotic solvent whereas others are polar protic solvents.

Question 10

Identify the glass equipment with ground-glass joints

Graduated pipette

Erlenmeyer flask

Buckner funnel

Separating funnel

Funnel

Correct Answer : d) Separating funnel

Explanation:

Glass equipments are divided into two; with ground-glass joints and without ground-glass joints. Separating funnel is the only glass equipment with ground-glass joints.

Question 11

The base peak in a mass spectrum is

The peak set to 100 % relative intensity

The peak set to 0 % relative intensity

The peak corresponding to the parent ion

The highest mass peak

The lowest mass peak

Correct Answer : a) The peak set to 100 % relative intensity

Explanation:

The most intense peak is called as base peak. It usually corresponds to the molecular ion only, if the spectra are recorded at low ionization energy.

Question 12

Which of the following is the weakest base?

CH3

H-F

H-Cl

H-Br

H-I

Correct Answer : e) H-I

Explanation:

The electronegativity and atomic size of iodine is larger so there is a weaker bond between hydrogen and iodine that makes the electron cloud much lesser than H-F bond. So, H-I is the weakest base; in other words it is the strongest acid.

Question 13

Which of the following shows the increasing order of solubility?

KCl

KCl

PbS

AgCl

AgCl

Correct Answer : b) KCl

Explanation:

KCl is highly soluble because its solubility is greater than 0.1M. AgCl is sparingly soluble because its solubility is less than 0.01 M. PbS is least sparingly soluble becauseits solubility is very much less than 0.01 M.